Container for fluids under pressure



April 1942- A. STEPHENSON 80,501:

CONTAINER FOR FLUIDS UNDER'PRESS'URE Filed Aug. 15, 1939 Sheets-SheetApril 21, 1942. A. STEPHENSON 12 5 CONTAINER FOR mums .UNDER PRESSUREFiled Aug. 15,' 1939 4 Sheets-Sheet 2 Fig 3.

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Moe/Mar.- Agyl'bur Stephenson 1 April 21,1942. AQSTEPHENSON Y I2,280,501

- CONTAINER FOR FLUIDS UNDER PRESSURE Filed Aug. 15, 1959 4 Sheets-Sheet5 'Fig. 9.

. [Carney p 21, 1942- I I A. STEPHENSON 28 CONTAINER FOR FLUIDS UNDERPRESSURE Filed Aug. 15, 1939 4 Sheets-Sheet 4 Fig. 17,

Fig. 16.

' lm entor: Arthur (Stephenson hgqm 4 Aktomey Patented Apr. 21, 1942UNITED STATES PAT-E NT ,OFFICE oon'mmnn ron FLUIDS UNDER.

rnnssunn Arthur Stephenson, London, England, assignor to The BritishOxygen Company England Limited,'London,

Application August 15, 1939, Serial No. 290,162

In Great Britain August 25, 1938 r 2 Claims.

sistance to stress of the weakest portion of the walls and, for anygiven internal fluid pressure, the weight of a container in relation toits internal volume is a minimum when the resistance of its walls tofluid pressure is uniform throughout the materials of which the wallsare constructed and the container is designed so that it may justwithstand the pressure to which it is subjected in use with the desiredor statutory margin for safety.

It is well known that for any given material of construction the weightof a containenin relation to its internal volume is a minimum when thecontainer is in the form of a hollow sphere and that fluid pressureacting on the internal surface of a'spherical container will produce a.material, or each of these in relation to the others, and although thecomputed values for these may vary slightly according to the formulaadopted in practice, it is conventionally accepted that the values ofthese factors in the case of a spherical container conform substantiallyto the law of the following equations:

nu f 42! wherein p=pressure t=thickness d=diameter f=stress It is alsowell known that if the container be in the form of a hollow cylinderwith closed endsthis being the more usual form of container employed inpractice for the storage and transport of fluids under pressurethedegree of stress in the material of the walls resulting from internalfluid pressure is not uniform as in the case of a spherical containerbutis greater in the circumferential direction than in the longitudinaldirection; for example, by simple conventional formula, the degree ofcircumferential stress or hoop tension is computable as:

and the degree of longitudinal or endwise stress is similarly computableas:

n! f 4t from which it is to be seen that whereas the longitudinal stressis of the same order as that which prevails under similar conditions inthe walls of a spherical container, the degree of circumferential stressin the cylindrical wall is computed to be twice as great. Consequently,in

order that the resistance to stress imparted by portion should be twicethat of the part spherical ,portions.

Similarly, in order that, for any given internal pressure, theresistance to longitudinal stress along the line of junction of anend-piece to the cylindrical body portion may be of the same order asthe resistance to circumferential stress, the minimum thickness ofmaterial required to connect the end pieces to the cylindrical portionis indicated to be half the calculated thickness of the cylindricalwall.

Therefore, in designing and constructing a cylindrical container so thatthe stresses in its walls may be uniform according to accepted method ofcomputation, the entire length of the body portion should have a wallthickness twice that of the part-spherical end pieces, and if soconstructed, the weight of the container in relation to internal volumeis to be regarded as a minimum for any given conditions of fluid pres-'sure and for the material employed in its construction.

Obviously, the weight of such a container in It is however, usual in themanufacture of cylindrical containers to form the body portionsufficient closure is produced. The concentration of material as theterminal portion of the tube is progressively reduced in diameterresults generally in a thickness of end piece appreciably greater thanthe wall thickness of the body portion of the container whereas,according to the above-mentioned formulae, it may be half the thickness.Where limitation in weight is an important consideration in the use of acontainer, the excess thickness of material in end pieces so formed is,insofar as is possibleand practicable, subsequently, removed, but theoperations mvolved are inconvenient and costly. The expense anddifliculties attaching to these operations are obviously increased andfrequently they become impracticable at the end which is entirelysealed;

in consequence, the weight .of the finished container remains excessive,and the stress in the material of the end piece is not uniform with thatof the body portion. I

Various methods of producing cylindrical containers of reduced weight inrelation to their internalvolume have been proposed, such priorproposals falling broadly into three groups. One proposal is toconstruct a container in which the thickness throughout is substantiallyequal to that required or computed for the end pieces and thereafter toreinforce the body port1on by applying to its external surfacestrengthemng material in the form of a sheath, windings of wire orseries of equally spaced or equal sized hoops.

Another proposal is to form deep corrugations in the container so thatit is comprised of a series of partial spheres or globular portionsjoined to-' gether by thickened necks of reduced diameters, or first toform a cylindrical container of nor- .mal thickness and then to subjectit to an exmined intervals, thereby forming a series of partial spheresor globular portions joined by necks of materials which remain at theoriginal thickness. D

A third proposal is to reduce the th ckness of the terminal portions ofthe tube so that it is less than that of the cylindrical portion beforeforming the contiguous end pieces.

None of the containers constructed in accord ance with such priorproposals possess a resistance to stress per unit area of the containerwalls including the reinforcing elements which would even approximate touniformity.

It is an object of the present invention to pro.- vide a substantiallycylindrical container for fluids under pressure in which the mass ofmaterial and/or weight thereof in relation to its internal volume is aminimum for any material or combination of materials of given or desireddegree of permissible working stresses.

It is another object of the invention to provide a cylindrical containerin which the reinforcement naturally resulting from the' end pieces, andwhich is transmitted for an appreciable distance along the body portion,is advantageously employed to reduce the amount of material required toimpart to the.body portion to provide a metal container of a novel andimproved character for the transportation and storage of fluids underpressure having a minimum of weight for a given volumeand a wallthickness which is different at different portions thereof in accordancewith the distribution of stresses.

The invention also contemplates an improved metal container for fluidsunder pressure having a minimum of weight for a given volume and havingreinforcing members incorporated therethe invention will become apparentfrom the present description taken in conjunction with the accompanyingdrawings, in which:

Fig. l is a central longitudinal section of a cylindrical containerconstructed in accordance with the invention on which is superimposed,for the purpose of comparison, a similar section of a standard type ofcylindrical container of equal internal volume as used heretofore;

Fig. 2 is a central longitudinal section of a cylindrical containerhaving reduced weight in accordance with the invention, the figure alsoshowing in dotted lines the extension of the body portion prior toformation of the end pieces therefrom;

Figs. 3, 4, 5 and 6 are central longitudinal part sections of modifiedforms of the container;

Fig. '7 is a central longitudinal section of a further modification;

Fig. 8 is a plan view partly in section of another modification; 1

Fig. 9 shows a part section of a cylindrical container strengthened bythe application of a reinforcing member;

Fig. 10 shows a constructional modification of the reinforcing membershown in Fig. 9;

Figs. 11 to 14 similarly show various modifications of reinforcingmembers as applied to the container;

Fig. 15 is a central longitudinal part section of another modified formof container;

Figs. 16 to 27 are part sectional views and end elevations of variousmodified forms of end portions of containers;

According to this invention there is provided for -fluids under.pressure a container comprising a substantially cylindrical body portionand an end piece constituting a closure member at each extremitythereof, the mass per unit area of the material constituting the bodyportion decreasing towards each extremity preferably in direct orapproximate proportion to the degree of reinforcement for stressresistance imparted to and transmitted along the body portion by andfrom the end pieces, the construction being such that the resistance tostress and dilation due to internal fluid pressure is substantiallyuniform throughout the body portion.

According to a furtherfeature of this invention, in a container forfluids under pressurecomprising a substantially cylindrical body portionand an end piece at each extremity thereof, the mass per unit area ofthe body portion decreasing towards each extremity, at least one endpiece is 2,280,561 I of a thickness less than that conventionallycomputed as required to withstand the fluid pressure to which thecontainer is subject in use and is provided with reinforcing meanswhereby the requisite resistance to stress due to internal pressure isachieved with minimum mass of material. By employing a containerconstructed in accordweight, the storage and transportation costs offluids stored therein may be substantially reduced.

In the design and construction of. containers according to theinvention, the -wall thickness at or about the longitudinal centre ofthe body porance with the invention so as to have reduced tion and thethickness of the'end pieces may be .determined empirically or computedin accordance with any convenient or accepted formula utilisingappropriate values for the allowable degree of stress in the material tobe used for construction of these as may be determined in an empiricalmanner from typical test containers subjected to appropriate internalfluid pressures.

Reinforcing members capable of acting also' as rolling hoops or impactand wear resisting memhers may be applied to the container and these maybe formed either integrally with'the material of the container or asseparate members and subsequently applied or attached to the preformedcontainer.

The diminution in thickness may be produced.

on the internal or external surface, or conjointly on both internal andexternal surfaces, and may be produced before or after attachment of theend pieces to or their formation from the bodyportion.

If the diminution is carried out before forming the end pieces, thedecrease in thickness may be extended either. progressively or inmodified degree to the extremities of the tubular or cylindrical bodypiece from which the contiguous end pieces are to be formed so as toavoid or limit excess of metal in the formed end pieces.

If the length of the body portion be short in relation to its diameter,for certain materials the normal calculated wall thickness of the bodyporsired shape, and may be convex, concave 01 convex-concave, and ofeither uniform or varying thickness, according to the shape of the endpiece preferred or required.

Inlet or outlet ports or connections, manholes,- and lifting or otherrequisite attachments may be arranged either in or on the end pieces oron the body portion.

The weight of the end pieces may be reduced by diminishing theirthickness from the outer diameter at or near the point of junctionbetween the and pieces and the body portion and towards the centre ofthe end piece either in steps as, for example-by a series of concentri Srecesses, or progressively, and the centre part may be left thicker forconvenient attachment of valve, or inlet and outlet connection or otherattachments.

Alternatively, the grooves or recesses may be formed to extend radiallyfrom the centre of an end piece to the periphery, in which case thegrooves may be formed by pressing or by addition to or removal ofsome ofthe material from the end piece during or after-manufacture thereof sothat spaced radial ribs or ridges of thicker metal capable ofreinforcing the end pieces remain be-' tween the recesses or grooves.Combinations of such radial and concentric reinforcing grooves or ribsmay be, of course, employed.

As a further alternative, the metal of the end piece maybe first made ofprogressively diminishing thickness from the periphery towards thecentre thereof, and' the radial grooves or recesses may besubsequentlvformed. For this pur-' pose, moulds may be applied to theend pieces acting against internal fluid or mechanical pressure, so'thatthe material is made to conform the shape provided in the mould. o

The provision of radial ribs and grooves or recesses can beadvantageously adopted in cases where the end pieces are of theconcavetype, which, in view of their shape, are partly housed within the bodyportion and which, unless of excessive weight as compared with theconvex type. have a normal tendency to invert and assume a convexhemispherical shape when subjected to internal fluid pressure.

The material of the finished container may, after completion, besubjected to suitable heat treatment for normalising, or hardening ortempering such as sorbitising, or certain parts, such as the outersurface of the body portion and/or the reinforcing or stiffening membersonly may be hardened or tempered to increase the stress hearingqualities I Alternatively, the heat treatments necessary to producetempering or hardening orconditioning of the material may be appliedonly to the portions which are of diminished or diminishing thickness,so that the material of the container may have greater ductility in itsthicker portions and/or in the reinforcing orstiflening members. Inanother method of carrying the improvements into effect in accordancewith the. invention, the bodyportion is formed with thinner walls, e. g.is only of suflicient thickness to withstand the longitudinal stress andis provided Preferably, the reinforcing sheath has maximum thicknessabout its central portion and tapers towards each extremity. Forexample, it

may be formed externally as a convex catena and internally as a tube ofparallel bore to conform 'to the external surface of the preformed bodyportion, so that when the sheath is fitted over the container, thegreatest thickness and strength is provided for a limited distance oneach side of the longitudinal centre. The sheath may be so used,-eachsuper-imposed sheath being of shorter length than the inside one itenvelopes so that greatest thickness results at or near the longitudinalcentre.

The sheath or sheaths may be fitted to the con tainer either bymechanical pressure or- "by shrinking on. If shrunk on, the sheath orsheaths may be heated for enlargement before passing over thethin-walled container, or the thin-walled container may be intenselycooled before insertin: it into the sheath.

In the case where wire winding is used instead of a'single or multiplesheath to provide the progressively increasing reinforcement inaccordance with the invention, the diameter of the wire may be greaterfor the winding at the centre and may diminish in stages as it extendstowards the end pieces. 'For this purpose wires of differentcross-sectional diameter and/or strengths may be either joined atintervals or left discontinuous and the windings may be made in separatesections with spacings therebetween or abut each other closely.Alternatively, th increase in strength of reinforcing material towardsthe longitudinal centre may be obtained b superimposing one or morelayers of wire winding of diminished or diminishing length so that thegreatest thickness of superimposed wire is disposed at or about thelongitudinal centre.

The windings may be held in position in rela tion to each other andlateral movement along the cylinder or turning movement aboutthecylinder prevented by any convenient means, such as by applying ametal or other suitable material of low melting temperature either'as a.brazing, solder, paint or cement-like filler of any sprayed on metal,and the material used for this purpose may be so selected and appliedthat it will serve as a protection against corrosion or like surfaceattack.

In order to ensure close fitting of the wire winding, the initialcontainermay be intensively cooled before the winding is applied, orprior to the application of each successive layer.

It is, however, not essential that the wire windings or the reinforcingsheath or sheaths apply pressure to any appreciable degree before thecontainer is subjected to internal pressure. For certain purposes. it ispreferable that the initial container be capable of expanding before thereinforcing members operate, provided that the exf pansion of theinitial container shall reasonably be within the elastic range of thematerial from which it is constructed.

In an alternative method of carrying out the invention the body portionof the container may be corrugated, the corrugations being soconstructed and arranged as to produce a progressively increasedstrengthening effect from the junction of the end portions with the bodyportion towards the longitudinal centre. The corrugations may becontinuous or separated by non-corrugated portions and may be parallelor helical, being preferably deeper and more steeply curbed towards thelongitudinal centre of the body portion.

It will be clearly understood that these various and alternative methodsof producing a container of the-cylindrical type. in which the resistance of the cylindrical portion to circumferential stressincreasestowards the longitudinal centre, lend themselves convenientlyto combinasuch a globular extension affords a reinforcing eifect whichcan be applied to reduce still fur-- ther the thickness of the taperingportion disposed between the end pieces and the globular extension.

Referring to Fig. 1, the usual known type of cylindrical container isformed from a tube having a central portion which constitutes the bodyportion l of the finished container and contiguous end pieces 5, I whichare produced by bending over and progressively reducing the diameter ofthe terminal portions of the tube. As shown inFig. 1, the concentrationof material at. for example, the end piece 8 due to the shapingoperation results in the thickness of the end piece 8 being considerablymorp than that of the body portion I from which it is formed; whereas,in accordance with the foregoing formulae, the end piece may be half thethickness of the body portion. The amount of material which may bedispensed with is shown in the dotted portion and the residual materialwhich constitutes a cylindrical container shaped in accordance with theinvention is shown by the hatched parts in Fig. 1.

From empirical determinations of containers of the two forms ofconstruction, it has been-ascertained that the saving in weight whichmay be effected by proceeding in accordance with the invention is of theorder of 36 to 0 per centum for containers of equal strength andinternal capacity.

. Referring to Fig. -2 of the drawings, a simple form of containerconstructed in accordance with the invention and having a weight inrelation to its contained volume which is less than that of containersof similar volume used hitherto, is formed from a hollow, andsubstantially cylindrical, body portion I. At its longitudinal centre 2,the body portion has a wall thickness either calculated according to theusual formulae or determined empirically for the degree of permissiblestress and dilation due to circumferential tension, and sections 3 and 4disposed between the centre section 2 and the end pieces whichprogressively diminish in thickness towards each extremity, so that whenthe end pieces 5 and 6 are formed from the thinner extremities of thebody portion, the thickness of wall at and/or adjacent tothe line ofjunction between the parts 1 and 5 at one end, and the parts 4 and t atthe further end, is substantially equal or approximates to the requisitewall thickness of the end pieces when calculated according to the usualformulae. If the end pieces 5 and 0 be hemispherical, they can besubstantially half the thickness of the centre section 2. In thepreferred design of the simple form of improved container, theprogressive diminution in thickness of the walls of the bodypiece I fromits longitudinal-centre 2 towards the end pieces results in the externalof the body piece having the shape of a convex catena as shown in Fig.6.

the precise form of which is preferably determined empirically fromtypical test cylinders subjected to appropriate pressures.

The end pieces which arepreferably of reduced thickness as compared withthe body portion may be varied in thickness to provide a suflicient eachside of the longitudinal centre.

- The amount of metal that can be so displaced ordispensed with withoutimpairing the effective strength of the body portion of the container isdependent upon its length in relation to its diameter; for example, ifwhen constructed of material normally employed for such containers thelength of the body portion be less than approximately diameters, it ispossible to reduce its weight to a further extent by reducing thethickness of wall at the longitudinal centre, in addition to theprogressive reduction in thickness towards the and pieces, because ofthe distance to which the reinforcing eifect of the end pieces istransmitted along the bod) portion. It has been found in practice thatthe approximate distance of 10 diameters varies also with thephyslcalproperties of the material.

In practice, however, it is necessaryto provide for variations inthickness of wall in consequence of the variations in thickness requiredfor normal tolerances on dimensions during manufacture. Unless theconditions of use merit the cost lb is accordingly caused to taper from2b towards lib. For the same reason, the portion 36 tapers towards thefurther extremity of'the container. Both ends may be globularor/hemispherical.

Instead of shaping the wall of the body portion so that it tapers fromthe central section towards the extremities, a cylindrical body portlonhaving a thickness no greater than is required for the end pieces may beused, and the body portion strengthened by a reinforcing member ormembers. I

As shown in Fig. 9, the reinforcing member may comprise a separatesheath I which tapers from the centre section'towards' each extremity.The form of taper may be that shown in any of Figs. 2, 3, 4, 5 and 6.Alternatively, a compound sheathing as illustrated in Fig. 10 may beemployed. V

In place of the sheathing 7, the reinforcing member may comprisewindings of wire lb arranged in superimposed layers. The windings may becontinuous as shown in Fig. 11, the number of layers being greatestabout the central section of the body portion and progressivelydecreasing towards each extremity. Alternatively, groups of multi-layerwindings lb may be provided as illustrated in Fig. 12, the number oflayers in each group decreasing from the centre sections towards eachextremity. Bands or collars 'lc, which may be shrunk-on, welded orotherwise secured to the body of the container, may

of manufacture to extremely small tolerance 1imitsfin thickness andconcentricity, it is necessary, and less costly, to allow reasonabletolerances on the limits of accuracy, and to reduce to a proportionateamount, for. example, 5 diameters, the length of body portion to whichany reduction in wall thickness at the longitudinal centre is eifected.In cases where the length of the body portion is considerable inrelation to diameter no metal is removed from the body portion for somedistance either side of the centre section 2, the wall of the centralzone 2a remaining parallel to the central longitudinal axis of the bodypiece asshown in Figs. 3, 4 and 5. The portions 3, 8 between the zone 2aand the end pieces may taper in a. straight line as shown in Fig.3, orin' steps as shown in of course, be used so long as the reinforcing ef-Fig. 4, or in acatenary curve as shown in Fig. 5.

If, in order to facilitate transport or for any other reason, it isdesirable that the exterior surface of the container be substantiallycylindrical, the inner wall may be made to taper towards the extremitiesas shown in Fig. 7. This may be accomplished either by removing materialfrom the internal surface or removing it from' the external surface andthen by well known means forcing the material inwards so that theexternal surface is made parallel.

In the modification shown in Fig. 8, the central section 2b is extendedinto a globular shape.

By reason of it possessing this shape, the thickness of the section 2bneed not be greater than that of the end piece 612, which may also beglobular. As thesphericity of the end piece 6b is greater than that ofthe section 2b, it is capable of imparting to the intermediate portionlb a larger reinforcing eifect and the portion be employefd asreinforcing members instead of wire windings. Fig. 13 shows onearrangement of collars 'Ic which vary in width, the widest being locatedabout the central section of the body portion and successively narrowercollars being disposed at progressively wider intervals towards eachextremity of the body portion. Fig. 14 shows an arrangement ofreinforcing members 7c similar to that shown in Fig. 13, but the collarsin this case decrease progressively in thickness towards each extremity.

The reinforcing members may be made of materials differing in tensilestrength, the material with the highest tensile strength preferably being disposed about the central section of the body portion, membershaving progressively lower and lower tensile strength being disposedbetween the central section and the terminal portions. .Any combinationof reinforcing members differing in dimensions and tensile strength may,

fect imported to the body portion is greatest about the central sectionand diminishes towards the end pieces.

In an alternative construction shown in Fig. 15, the thickness of thecentral portion may be reduced as compared with that shown in Figs. 1 to6 and without the necessity of providing any reinforcing members, byforming a central corrugation 2c and complementary corrugations 8, 9 atthe junctions of the end pieces with the body portion, the intermediateportions 30 and 4c tapering from the corrugation 2c towards eachextremity. It will, of course, be understood that the number ofcorrugations is not limited to that shown.

Containers having a body portion which tapers in thickness towards theend 'pieces as hereinbefore described may also be corrugated to provideany desired reinforcement. These corrugations may be of uniform pitchand depth'or they may vary in pitch and/or depth to impart a varying. A

degree of reinforcement to different parts of the body portion so as tomaintain uniformity in the resistance to stress and dilation due tointernal fluid pressure.

, Similarly, the reduction in weight of the end pieces is dependentupon/or corresponds to the amount of metal displaced or dispensed witheither before or after forming the end pieces. The amount of metal thatcan be displaced or dispensed with is'dependent upon the form of endpiece to be employed. The hemispherical form made from extremities ofthe body portions which have been previously reduced in thickness ismost convenient to'manufacture and affords the greatest volume inrelation to weight more especially if its thickness is furtherdiminished towards the centre, but circumstances or conditions of userequently require that the shape of the end piece shall be concave orconvex-concave, ellipsoidal, flat or other convenient shape. In thiscase concentric or radial grooving or the formation of radial ribs orfins permits of part of the end piece to be of reduced thickness toeffect closure and disposes the metal of the reinforcing elements insuch a position that maximum reinforcement is afforded with minimumweight.

Various forms of end pieces shaped in accordance with the invention areillustrated in Figs. 16 to 27.

As shown in Fig. 16, the end piece 6 is hemispherical and of uniformthickness less than that of the terminal portion 4 of the body por--tion. Where the end piece 8 is less than hemispherical the thicknessthereof may progressively decrease towards the centre as shown in Fig.

When the end piece 6 is fiat as shown in Figs. 18 and 19, it may bereinforced by a plurality of substantially hemispherical or otherconveniently shaped radial buttress ribs l extending diametricallyacross the base of the container,

the ribs having the greatest depth at the middle. When the end piece 8is concave, it may be reinforced by a plurality of radial buttress ribslilalextending diametrically across the concave portion as shown inFigs. 20 and 21. Figs. 22 and 23 show similar reinforcement achieved byproviding radial ribs [0b with a centre boss H to permit either of theformation of an inlet or outlet connection or the attachment of liftingor other means.

Where the end piece 6 is convex, radial ribs [0c may be provided asshown in Figs. 24 and 25,

the ribs increasing in depth to a maximum at the middle. If a convex endpiece has initially a greater thickness than is necessary to withstandthe iuternal fluid pressure to which the container is subject in use,annular grooves may be formed in the-end piece, the depth and/or widthof the grooves increasing towards the centre of the end piece. As shownin Figs. 26 and 27, the grooves may be V-shaped as shown at llld, andthese may be supplemented by radial ribs such as illustrated in thepreceding Figs. 18 to 25.

It will be clear that containers constructedv from metallic materials ofcomparatively low tensile strength and which, to provide adequatestrength in the central part of the cylindrical Such materials, forexample, mild steels, usually have greater shock resistance and a higherde-- gree of ductility than high carbon or alloy steels; moreover, theyare less costly and have the added advantage that they are usually lessdiiilcult to manipulate in the processes of manufacture and heattreatment.

It will, of course, be understood that, whereas, the improvements mayshow greater advantage in materials of lower degrees of stressresistance, they are equally applicable tomaterials of; high degree ofstress resistance. Further, the improvements hereinbefore proposed maybe applied for the same purpose and advantage to containers designed andconstructed according to present practice and which may even havealready been in service for the storage and/or transport of fluids underpressure.

I claim:

1. A container adapted for the storage of fluids under pressurecomprising a substantially cylindrical body portion formed from a singlehomogeneous tubular member, and an end piece at each extermity of thebody portion constituting a closure member, said end pieces being formedintegrally with the'body portion by progressive reduction in diameter ofthe material of the body portion, the mass per unit area of the materialconstituting the body portion decreasing towards each extremitysubstantially in proportion to the degree of reinforcement forresistance to stress and dilation imparted to and transmitted along thebody portion by the end pieces, said decrease in mass being effected bya progressive reduction in thickness of the body portion whereby theresistance to stress and dilation due to internal fluid pressure issubstantially uniform throughout said body portion, and wherein theprogressive reduction in thickness of the body portion is stepped atappropriate intervals. v v

2. A container adapted for the storage of fluids under pressurecomprising a substantially cylindrical body portion formed from a singlehomogeneous tubular member, and an end piece at each extremity of thebody portion constituting 'a closure member, said end pieces beingformed integrally with the body portion by progressive reduction indiameter of the material of the body portion, the mass per unit area ofthe material 4 constituting the body portion decreasing towards eachextremity substantially in proportion to the degree of reinforcement forresistance to stress and dilation imparted to and transmitted alon thebody portion by the end pieces, said decrease in mass being effected bya progressive reduction in thickness of the body portion whereby theresistance to stress and dilation due to internal fluid pressure issubstantially uniform throughout said body portion, and wherein the bodyportion has a substantially cylindrical internal surface, and whereinthe progressive reduction in thickness of the body'portion is effectedexternally.

ARTHUR STEPHENSON.

